1. Field of the Invention
The present invention relates to a grease composition, which hardly disperses and has excellent high-temperature performance. Moreover, the present invention relates to a rolling apparatus, which has low torque and excellent acoustic performance and generates a few dusts, and in particular, the present invention relates to a rolling apparatus, which is preferably used in electronic intelligence equipment, semiconductor manufacturing machines and others.
Furthermore, the present invention relates to a grease composition having excellent lubricating ability and heat resistance. Still further, the present invention relates to a rolling apparatus, which has excellent lubricating ability and is long-lived under high-temperature conditions, and in particular, it relates to a rolling apparatus, which is preferably used as a rolling or sliding portion of machines used under high-temperature and high-speed conditions including car electrical components such as alternators or electromagnetic clutches; auxiliary equipment for car engine such as idler pulleys; and business machines such as copying machines or printers.
Furthermore, the present invention relates to a grease composition having excellent rust protection, extreme-pressure property, water resistance and lubricating life, and a rolling apparatus which is long-lived although it is used under stringent conditions.
Furthermore, the present invention relates to a grease composition having excellent heat resistance, lubricating ability and rust protection. Still further, the present invention relates to a rolling apparatus which has excellent lubricating ability and is long-lived under high-temperature conditions, and it particularly relates to a rolling bearing, which is preferably used in electrical machines for a car engine which are required for heat resistance, load carring capacity and durability.
Furthermore, the present invention relates to a grease composition having excellent lubricating ability and electric conductivity. Still further, the present invention relates to a rolling apparatus, which has excellent electric conductivity and is long-lived under high-temperature conditions, and in particular, it relates to a rolling apparatus, which is preferably used as a rolling or sliding portion of machines used under high-temperature and high-speed conditions including car electrical components such as alternators or electromagnetic clutches; auxiliary equipment for car engine such as idler pulleys; and business machines such as copying machines or printers.
2. Description of the Related Art
(1) A rolling apparatuses (e.g. rolling bearings, linear guide apparatuses, ball screws, etc.), which are used in electronic intelligence equipment such as a hard disk drive (hereinafter referred to as HDD) or laser beam printer (LBP), semi conductor manufacturing machines and others, are required to have various performances such that these apparatuses generate a few dusts, have low torque and excellent acoustic performance, and are long-lived.
Moreover, with the development of high-precision electronic intelligence equipment and semiconductors in recent years, the use conditions (temperature, speed, etc.) of rolling apparatuses, which are used in electronic intelligence equipment and semiconductor manufacturing machines, have become increasingly strict. Under such strict use conditions, the above stated various types of performance are required to be excellent.
For example, in the case of electronic intelligence equipment such as HDD used under a clean atmosphere, if a gaseous oil or the fine particles of grease are released from the inside of a bearing when a rolling apparatus rotates, the fine particles pollute a recording medium or the like and cause operation errors. Therefore, it is most important to suppress the amount of dusts generated.
As a grease composition enclosed in such a rolling bearing for HDD, Undock C (Trade name), which is a grease comprising a mineral oil as a base oil and a sodium complex soap as a thickener, is well known, and this product has been used over 20 years because it causes a small amount of dusts.
When excellent performance of low torque and low noise is required, a grease comprising a lithium soap as a thickener and an ester oil as a base oil has been used at times.
Moreover, Japanese Patent Laid-Open No. 2000-109874 discloses a fluoro grease composition obtained by mixing a silicone oil into a fluoro grease consisting of a fluoro oil and a thickener. This fluoro grease composition has a property such that oil does not leak so much from the grease.
Furthermore, Japanese Patent Laid-Open No. 2001-187892 discloses a grease composition comprising a silicone oil as a base oil, polytetrafluoroethylene as a thickener, silica aerogel and an extreme-pressure additive. This grease composition has a property such that it has excellent low-temperature flow property, wear resistance, heat resistance and low torque property at a low temperature.
However, in the above sodium complex soap-mineral oil grease, the dispersibility of the thickener is insufficient and so it hardly becomes homogenous, and thereby problems regarding acoustic and vibration performances occur in the early stage of rotation of the rolling bearing. In addition, since this grease has strong hygroscopicity and gets hard over time, and thereby the flow property in the rolling bearing decreases, this grease also has a problem of causing insufficient lubrication and readily generating abnormal sounds from the cage.
Therefore, when excellent performance of low torque and low noise is required, the above described lithium soap-ester oil grease has been used at times. However, since this grease easily disperses (causes a large amount of dusts), there is a great risk that the grease might pollute a recording medium or the like when it is used in a rolling bearing for HDD. Moreover, since the temperature used for the rolling bearing for HDD is more and more increased, the above described lithium soap-ester oil grease cannot be applied in some cases.
Further, the grease compositions as disclosed above in Japanese Patent Laid-Open Nos. 2000-109874 and 2001-187892 comprise a very expensive silicone oil or fluoro oil, these grease compositions are expensive when compared with common greases.
Thus, it is a first object of the present invention to solve the above described problems of the prior art techniques and to provide a grease composition which is hardly dispersed and has excellent high-temperature performance. Moreover, it is also the first object of the present invention to provide a rolling apparatus, which has low torque and excellent acoustic performance, and generates a few dusts.
(2) Cars (passenger cars) tend to be directed towards downsizing, weight saving and the expansion of the living space, and therefore cars are forced to reduce their engine room space. For this reason, the downsizing and weight saving of electrical components or auxiliary equipment for car engine are increasingly progressing. In addition, cars are required for silence improvement, the hermeticity of the engine room is progressing, and thereby the temperature in the engine room becomes higher. Accordingly, the above described components or equipment for cars are also required for high-temperature resistance property. For example, bearings for electrical fan motors had previously been used at a bearing temperature of 130° C. to 150° C., but in recent years, the same bearings have been required to resist a high temperature of 180° C. to 200° C.
As described in Japanese Patent Publication No. 2977624, bearings used under high-temperature environment of 150° C. or higher have previously been dealt with by filling the inside of the bearing with a grease obtained by mixing a lithium soap and a urea compound into a synthetic oil type lubricating oil. However, under a high-temperature condition of 160° C. or higher, even this grease generates seizure in an early stage, and so a grease having further higher heat resistance is required.
On the other hand, in OA machines, especially in copying machines or the like, since color fine particles (toner) consisting of a thermoplastic resin and a coloring agent is fused by heating and then fixed on a paper by pressure, a heater is inserted into the axis of a roller, and therefore the temperature of the rolling bearing of a bearing portion sometimes rises to 140° C. to 200° C., depending on the models. Therefore, for such rolling bearings, a grease having excellent heat resistance should be used.
For example, a fluoro grease comprising polytetrafluoroethylene (PTFE) as a thickener and a perfluoropolyether oil (PFPE oil) as a base oil has excellent heat resistance, and so a rolling bearing filled with this fluoro grease can be used under high-temperature environment of 160° C. or higher.
However, since it is difficult to add additives that can be mixed into common greases into the above described fluoro greases, these greases are likely to have poor lubricating ability, rust protection and a metallic corrosion preventing property. Moreover, the fluoro greases have another disadvantage in that these greases are more expensive than synthetic oil type greases by approximately 5 to 20 times.
Japanese Patent Laid-Open No. 11-181465 describes a grease composition, heat resistance of which is improved by blending a fluoro oil with a urea grease. However, since a mineral oil or synthetic oil that is a base oil of the urea grease has a poor affinity for a fluoro oil, the above grease composition has a high oil separation percentage, and therefore this grease composition has a disadvantage in that the use of the grease composition is inappropriate for a bearing used in components which rotate at a high speed.
Thus, it is a second object of the present invention to solve the above described problems of the prior art techniques and to provide a grease composition having excellent lubricating ability and heat resistance. Moreover, it is also the second object of the present invention to provide a rolling apparatus, which has excellent lubricating ability and is long-lived under high-temperature conditions.
(3) With the development of mechanical technology in recent years, mechanical devices tend to be directed towards downsizing, weight saving and high-speed rotation. Mechanical portions such as a bearing and a gear become increasingly exposed at a high temperature. Therefore, in such mechanical portions, a grease used at a high temperature is used. Moreover, a grease used at a high temperature is used also for bearings which are used under high-temperature conditions, such as bearing integrated into iron manufacturing machines (e.g. continuous casting machines, rolling mill for iron and steel, etc.,) various heat processing apparatus or driers.
Examples of such a high-temperature grease include a metallic soap grease which uses, as a thickener, a metallic soap such as Ca, Al, or Li, and a complex metallic soap; an organic grease which uses an organic compound such as polyurea, a terephthalamic acid metal salt or a fluoro resin; and an inorganic grease which uses an inorganic compound such as bentonite.
However, each of these greases also has a disadvantage. For example, the metallic soap grease such as an alminum complex grease has excellent lubricating ability, but it cannot maintain the grease structure for a long time under high-temperature conditions. The grease comprising polyurea is likely to cause hardening phenomenon, and the grease comprising a terephthalamic acid metal salt has large oil separation. Further, the grease comprising bentonite has insufficient rust protection, extreme-pressure property and water resistance.
As a grease which solves the above problems, a grease obtained by adding dibasic acid esthers into organic bentonite to enhance rust protection is known (Japanese Patent Laid-Open No. 6-200273). There is also known a grease obtained by adding the metal salt of carboxylic acid with a substitution at condensed ring into organic bentonite to enhance a metallic corrosion preventing property (Japanese Patent Publication No. 2711150).
However, the grease described in the above Patent Publication still has a problem regarding insufficient extreme-pressure property and water resistance.
Thus, it is a third object of the present invention to solve the above described problems of the prior art techniques and to provide a grease composition having excellent rust protection, extreme-pressure property, water resistance and lubricating life. Moreover, it is also the third object of the present invention to provide a rolling apparatus, which is long-lived although it is used under strict conditions.
(4) As stated above, with the development of mechanical technology in recent years, mechanical devices tend to be directed towards downsizing, weight saving and high-speed rotation, and rolling bearings used in electrical machines surrounding a car engine also tend to have a high temperature. On the other hand, resources and power saving efforts are required, and maintenance-free mechanical devices are also required. Accordingly, rolling bearings are required not only for heat resistance but also for reliability and durability.
Presently, in rolling bearings used under high-temperature environment over 180° C., a fluoro grease, clay mineral grease or the like is generally charged. However, although these greases are excellent in heat resistance, they have a disadvantage in that they have poor lubricating ability, load carring capacity and rust protection.
As a grease satisfying conditions such as rust protection, heat resistance and load carring capacity, a calcium sulfonate complex grease which comprises, as a thickener, a calcium sulfonate complex containing calcium carbonate is known (Japanese Patent Publication No. 5-8760). However, when this calcium sulfonate complex grease is used under high-temperature conditions over 180° C., it does not have the same level of heat resistance as a fluoro grease.
Thus, it is a fourth object of the present invention to solve the above described problems of the prior art techniques and to provide a grease composition having excellent heat resistance, lubricating ability and rust protection. Moreover, it is also the fourth object of the present invention to provide a rolling apparatus, which has heat resistance so that it can be used under high-temperature conditions over 180° C., as well as having excellent load carring capacity, durability and rust protection, and particularly to provide a rolling bearing which is preferably used in electrical machines surrounding a car engine.
(5) Cars (passenger cars) tend to be directed towards downsizing, weight saving and the expansion of the living space, and therefore cars are forced to reduce their engine room space. For this reason, the downsizing and weight saving of electrical components or auxiliary equipment for car engine are increasingly progressing. In addition, cars are required for silence improvement, the hermeticity of the engine room is progressing, and thereby the temperature in the engine room becomes higher. Accordingly, the above described components or equipment for cars are also required for high-temperature resistance property.
At present, as a grease composition used for the rolling bearing of each of the above components, a grease composition comprising a synthetic oil as a base oil and a urea compound as a thickener is mainly used, and this urea compound-synthetic oil grease has excellent lubricating ability up to a temperature of 170° C. to 180° C. However, under high temperature conditions of 200° C. or higher, the evaporation of the base oil, the hardening of the grease associated therewith, and the softening of the grease by the construction of the thickener occur, and therefore there is a risk that a rolling bearing filled with the urea compound-synthetic oil grease might generate seizure in an early stage.
Moreover, as described in Japanese Patent Laid-Open No. 11-72120, in the rolling bearing used in each of the above components, there are some cases where hydrogen generates by water present in the bearing, and the generated hydrogen enters in a bearing steel constituting an inner ring, an outer ring and rolling elements, thereby causing a flaking of formed white structure due to hydrogen brittleness. This is considered to occur as a result of the phenomenon that a direct electric current is generated by metallic contact by vibration or the like at a portion between the inner and outer rings which becomes isolated by the oil film of a lubricant, and that hydrogen ions thereby generate from the water present in the bearing. The generation of hydrogen and the flaking of formed white structure thereby can significantly be controlled by the impartation of electric conductivity to a grease.
On the other hand, in OA machines, especially in copying machines or the like, since color fine particles (toner) consisting of a thermoplastic resin and a coloring agent is fused by heating and then fixed on a paper by pressure, a heater is inserted into the axis of a roller, and therefore the temperature of the rolling bearing of a bearing portion sometimes rises to 140° C. to 200° C., depending on the models. Therefore, for such rolling bearings, a grease having excellent heat resistance should be used.
Moreover, as described above, since the inner and outer rings of a rolling bearing become isolated by the oil film of a lubricant, static electricity generates by rotation. Since the radiation noise has adverse effects such as distortion on the copying screen of a copying machine, as described, for example, in Japanese Patent Publication No. 63-24038, there is taken a countermeasure of charging a grease with electric conductivity in a rolling bearing to electrify the portion between inner and outer rings, thereby eliminating static electricity.
For example, a fluoro grease comprising polytetrafluoroethylene (PTFE) as a thickener and a perfluoropolyether oil (PFPE oil) as a base oil has excellent heat resistance, and so a rolling bearing filled with this fluoro grease can be used under high-temperature conditions of 180° C. or higher.
However, since it is difficult to add additives that can be mixed into common greases into the above described fluoro greases, these greases are likely to have poor lubricating ability, rust protection and a metallic corrosion preventing property. Moreover, the fluoro greases have another disadvantage in that these greases are more expensive than synthetic oil type greases by approximately 5 to 20 times.
Japanese Patent Laid-Open No. 11-181465 describes a grease composition, heat resistance of which is improved by blending a fluoro oil with a urea grease. However, since a mineral oil or synthetic oil that is a base oil of the urea grease has a poor affinity for a fluoro oil, the above grease composition has a high oil separation percentage, and therefore there is a disadvantage that the use of this grease composition is inappropriate for a bearing used in components which rotate at a high speed.
Thus, it is a fifth object of the present invention to solve the above described problems of the prior art techniques and to provide a grease composition having excellent lubricating ability and electric conductivity. Moreover, it is also the fifth object of the present invention to provide a rolling apparatus, which has excellent electric conductivity and is long-lived under high-temperature conditions.
(6) As stated above, grease composition are classified into the following 4 types according to the types of a thickener:
(i) a metallic soap grease comprising a metallic soap such as Li, Ca, Na or Al;
(ii) a complex metallic soap grease comprising a complex metallic soap such as Li, Ca, Na and Al;
(iii) an organic grease comprising an organic compound (an organic thickener) such as polyurea, a terephthalamic acid metal salt or a calcium sulfonate complex; and
(iv) an inorganic grease comprising an inorganic compound (an inorganic thickener) such as bentonite or silica gel.
However, as described in the “Lubrication Control Manual Book” edited by the Japan Lubricating Oil Society and the Lubrication Control Diffusion Task Force (the Japanese Lubricating Oil Society, published Mar. 20, 1990) and “A Brief History of Lubricating Greases” written by Arthur T. Polishuk (Llewellyn & McKane, Inc., published 1998), it has previously been thought that, when different types of grease compositions are mixed, the properties of the grease compositions are altered and deteriorated in many cases. This deterioration naturally occurs when 2 types from among the above 4 types of grease compositions are mixed, but it could also occur when 2 types of metallic soap greases are mixed, in which the type of metals is different.
When a significant deterioration occurs in a grease, the grease structure is destroyed, significant softening of the grease or decrease of the dropping point occurs, and the grease is liquefied at times. Moreover, there are also cases where additives which are added to a grease composition, act on one another and reduce the performance of the grease composition. For these reasons, it has generally been believed that the mixing of grease compositions should be prevented as much as possible.
Grease compositions used in rolling apparatuses such as a rolling bearing, a ball screw, a linear guide apparatus and a linear bearing are required to have various performances such as lubricating performance, load carring capacity, heat resistance, water resistance, low torque and few dusts generating property. To obtain such a grease component having many excellent performances, a method for mixing grease components each having one of the above performances is considered to be effective. However, probably because it has generally been believed that the mixing of grease components comprising different types of thickener is not good, the above method has seldom been used.
A few examples include Japanese Patent Publication No. 6-31375 disclosing the combined use of an N-substituted terephthalamic acid metal salt and polyurea, Japanese Patent Laid-Open No. 7-268370 (& U.S. Pat. No. 5,948,737 A) disclosing the combined use of a hydrogen-addition grease and a fluoro grease or fluoro oil, and Japanese Patent Laid-Open No. 2001-3074 disclosing the combined use of a sodium soap and a lithium soap.
Although two types of thickener are used in combination, if the excellent performances of both thickener consist with each other, the above described grease component having many excellent performances can be obtained. Thus, the present invention adopts a method involving the combined use of two different types of thickener to achieve the above described first to fifth objects.